1. Field of the Invention
This invention relates in general to the deposition and growth of materials on substrates. More specifically, the invention relates to a method and associated apparatus that rapidly and consistently produces deposited layers having improved film properties using ion beam deposition in combination with DC and RF sputtering.
2. Description of Related Art
Known giant magnetoresistive (GMR) read/write heads are composed of multiple thin films, including a sensing layer, a pinned layer, and an exchange layer. GMR heads have been increasingly utilized in recent years because of their spin valve effect, which significantly increases data read/write rates and densities. A spin valve, in general, consists of a GMR trilayer with layers as described above. The sensing layer is magnetically soft, or very sensitive to small fields. The pinned layer is made magnetically hard, such that it is insensitive to fields of moderate size. The magnetic orientation of the pinned layer is fixed and held in place by the adjacent exchange layer, while the magnetic orientation of the sensing layer changes in response to the changing magnetic field of the disk. A sandwich structure of this type, having two ferromagnetic layers separated by a nonmagnetic metallic layer with the magnetization of one of the ferromagnetic layers pinned, constitutes a spin valve magnetoresistive sensor (SVMR). As the soft free layer moves in response to applied fields, the resistance of the whole structure will vary. This is known as the spin valve effect, and it renders GMR heads highly sensitive to magnetic fields from the disk. The increased sensitivity translates to detection of smaller recorded bits at higher data rates than are normally realized, making GMR heads favorable in the development of read/write technologies.
In the manufacture of thin film magnetic recording heads or disks, various prior art methods are used to deposit series of layers on a substrate disc. These known methods can include electroplating, thermal evaporation, chemical vapor deposition (CVD), molecular beam epitaxy (MBE), ion beam deposition (IBD) and physical vapor deposition (PVD), among others. PVD involves acceleration of ions from plasma toward a target. Bombardment with the ions releases material from the target which is then deposited on the disc, or wafer. A common PVD method is known as cathodic sputtering.
In known sputtering processes, a target made of the deposition material is aligned with the substrate in a sputtering chamber. A gas, for example argon, is introduced into the sputtering chamber where it is ionized and the resultant ionized particles accelerate toward the target, which has a negative bias applied to it. The ion bombardment causes some of the target material to break off, or sputter, from the target. The sputtered material is directed to the substrate and deposited thereon.
There are two common sputtering methods known in the art: DC magnetron and radio frequency (RF). In DC magnetron sputtering, a negative DC voltage is applied to the target. A magnetic field confines the plasma to the target. DC magnetron sputtering yields favorable sputtering rates that are relatively high and produce deposited films quickly, but has limited target utilization as only portions of the targets are activated. In contrast, RF sputtering, which may be carried out with or without the presence of a magnetic field, applies a radio frequency voltage to the target and/or to the substrate to achieve a net negative bias on the target. While RF sputtering yields higher target utilization, the sputtering rates are much lower and hence deposit film layers more slowly. In fact, DC magnetron has a deposition rate up to 50% higher than that of RF magnetron.
Long known drawbacks common to both DC and RF sputtering include the presence and buildup of plasma around the target and the substrate, and contamination of the chamber. Plasma buildup lowers the efficiency of sputtering and may also contaminate the layers. In the sputtering methods, plasma is in contact with the target and substrate and is, therefore, strongly influenced by it. Any changes to the target surface or substrate, which are difficult to control, affect the plasma and, therefore, also affect the properties of the film. Furthermore, plasma can be influenced by the substrate magnetic fields used to orient the magnetic field during deposition.
A prior art method that avoids the complexities known in the art, including plasma buildup and those previously described, is ion beam deposition (IBD). IBD is a materials growth technique in which thin films are deposited onto a substrate from a target, using low energy ions. IBD uses lower operating pressure which results in less impurity incorporation in the deposited films and less scattering of sputtered particles. Also, the plasma is confined in the ion gun, and the ions are directed only to the target area, avoiding contamination of the chamber and buildup of plasma. This avoids complexities created by plasma target and substrate plasma interactions.
While conventional IBD separates plasma from target and substrate, limits cross contamination of target materials and overcomes other disadvantages associated with RF and DC magnetron sputtering, it too has its own drawbacks. Although an ion source used in IBD may be used for the deposition of any material, the deposited materials have higher energies in comparison with conventional RF/DC sputtering. In ion beam sputtering, the deposited particles are not thermalized, while RF/DC deposited particles have lower energy due to scattering. Clearly, both RF/DC and IBD have unique advantages and disadvantages.
More recently, mixture type spin valve deposition systems are known in the art that utilize both IBD and RF and DC sputtering processes. These systems seek to utilize the advantages of both types of material deposition. The film structures produced by these combined systems are contemplated to have improved spin valve characteristics. However, the known mixture type systems also have inherent limitations of their own. The mixture type systems utilize separate chambers for the different deposition processes. In the mixed system, the two type chambers (ion and conventional RF or DC) are connected by a robot chamber. Between layer depositions in either of the deposition chambers, the substrates travel on a robot arm through the interconnecting robot chamber. Travel between the two deposition chambers typically lasts between 3 and 5 minutes.
In very high vacuum research systems, base pressures in the vacuum chamber are in the 10xe2x88x9210 torr range. However, in development and manufacturing type systems, the robot chamber typically has a base pressure in the 10xe2x88x927 torr range. At this pressure, some amount of background gas such as water vapor, inherently present in the atmosphere, is deposited on the surface during each minute that the substrate is in the robot chamber. The layers of background gas will degrade the film properties and reproducibility of film production results.
It is therefore a purpose of the present invention to improve the limitations inherent to known thin film deposition manufacturing methods. More specifically, it is a purpose of the present invention to eliminate the step of transfer between deposition chambers and the associated exposure of growing film structures to unsuitable base pressures currently in known multichamber deposition systems.
The method and apparatus of the present invention combine IBD and sputtering processes in a single chamber to create a new materials manufacturing system. The present invention substantially reduces and even can eliminate the problems associated with known multiple chamber deposition processing while utilizing various deposition methods to claim their various advantages. The Merged Spin Valve Deposition System (MSVDS) allows the manufacture of spin valve film structures by two or more separate deposition methods with the elimination of substrate travel in a low vacuum chamber. The invention truly maintains the benefits of the different known deposition methods while eliminating the use of multiple chambers, the exposure to undesirable, elevated base pressures, and the deleterious effects on growing film surfaces due to contamination during substrate travel. The invention also eliminates associated complexities, exposure, and production delays associated with it. Moreover, the invention allows a previously unknown high throughput process for the manufacture of deposited thin film layered structures.
The foregoing and other objects, features, and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments which makes reference to several drawing figures.